[Nsgrn]

I need some advice on plug selection, or tuning tips.
Picture shows my plugs from cylinders 1,2 but all look relative the same. They are Autolite 85's. These are in a street driven 400 with 48 heads. From research reading internet information the condition on them compare to cold-rich but ok. Carb and timing tune are the best I can get. The carb is a modified 750dp with no choke horn, so I have to lean into the throttle a bit on cold starts. Timing is 16 intial with the factory HEI 20 picking up the rest, no vac advance.

Reason for asking is I installed headers yesterday, was running stock manifolds from a 68 400. Now it seems I have a cylinder mis, or the sound change is throwing me for a loop. The engine is smooth when easing into the throttle at the carb linkage, just the sound out the rear is a noticeable difference. Its not an exhaust leak or plug wire mix-up issue.
I am going to do a valve adjustment before proceeding with the plug or fire issue. Nothing was changed during the header manifold swap.

[Blued and Painted]

Its easy to crack the plug insulator when doing manifold work. Which could cause an intermittent skip.
Heat range looks good IMO.

[Nsgrn]

That is a good tip. The passenger side was a PITA getting to position. The flange was pressing against number 2 plug at one point trying to wedge it up in there. Thanks